The present proposal is a fundamental research program to study systematically diffusional and interfacial phenomena between the phases existing during amalgamation process in dental alloys. The research relies principally on the use of radioactive tracers, a topic on which the present investigator has experience and publications. Data on diffusion properties in the multiphase-multicomponent system in question will be obtained for the three metals (silver, tin and mercury) that are the principal components of dental amalgams. The compositions studied include Ag3Sn, gamma1 (Ag3Hg4), gamma2 (HgSn7-8), and mercury. The research effort for the current year was concentrated on studies of the diffusion and interfacial reactions between gamma1 and Ag3Sn and gamma2 and Ag3Sn. Very significant results were obtained in the reactions between the above compounds. Further investigations by, for example, X-ray diffraction technique are under progress.